The Department of Human Services Public Health office of Environmental Toxicology evaluates bluegreen algae test data to determine whether algal blooms present hazards to animals or human beings. DHS does not have resources to collect or test algae samples, but DHS often receives reports of testing done by private contractors, researchers or other government agencies.

Why are advisories issued?

Algal blooms are common in surface waters throughout Oregon, and generally blooms contain many species of algae. Most algae are harmless, but there are several species of bluegreen algae (also known as cyanobacteria) that may produce toxins that are potentially harmful. In Oregon the primary algae’s of concern are Microcystis and Anabaena. Others may be identified in the future.Advisories are issued by DHS when cell counts exceed certain limits or when potentially harmful toxin levels are found. Toxins in water may be absorbed by humans when swallowed, and when inhaled as droplets or spray in the air. Pets and domestic animals are at risk as well as human beings.

Advisories may include warnings against ingesting water, swimming or bathing, or inhaling water droplets. Advisories may also include information about treating water to reduce or eliminate toxins.

How long do advisories last?

Dangerous algal blooms may develop and disappear within a matter of days, or they may continue for weeks or months. The longest advisory period for any water body in Oregon to date began in early June and lasted into late November. The intensity of the bloom and the concentrations of toxin in a water body are not uniform. Often the algae are most dense around the edges of the water body, but wind or water currents may change the location of affected areas very quickly.

Usually a dangerous bloom is associated with a distinct bluegreen color and cloudiness in the water. Algal blooms often produce large floating masses of green, yellow or bluish green slime. Visibly affected water should be avoided whether or not there is an official advisory in place.

FAQ about bluegreen algae can be found here with pictures of the algae: